Gas blocking device for optical fiber repeater

ABSTRACT

A gas blocking device is used in an optical fiber repeater or other device to prevent the passage of gas, for example, to prevent nitrogen from escaping from a pressurized housing through a fiber holding tube or pigtail. The gas blocking device includes a fiber containing body, a fiber organizing insert, and a locking member securing the insert to one end of the body. The fiber containing body is attached to one end of the fiber holding tube. The fibers extend from the fiber holding tube through a passageway in the body, and each of the fibers extends through a fiber receiving hole in the fiber organizing insert. The insert engages the body such that the insert is prevented from rotating with respect to the body and the fibers are protected against microbending and other damage. A material, such as hot melt glue, fills at least a portion of the body and surrounds the fibers to block the gas from entering the fiber holding tube.

TECHNICAL FIELD

[0001] The present invention relates to fiber optic systems and, moreparticularly, to a gas blocking device used to permit the passage ofoptical fibers while preventing the passage of gas therethrough.

BACKGROUND INFORMATION

[0002] Repeaters are commonly used in fiber optic systems to amplifyoptical signals being transmitted over long distances. A repeater bodyis coupled to a fiber optic cable at each end. The repeater body houseselectronic circuitry and lasers used to amplify the optical signals.Lasers and electronics housed in the repeater body should be maintainedunder very dry conditions, because the slightest amount of condensationin the repeater can cause arcing. Arcing can be devastating to theoperation of the system. Maintaining these very dry conditions is mostimportant in undersea applications but also applies as well toterrestrial applications.

[0003] To achieve these dry conditions, prior to installation, therepeater housing is vacuum drawn and the air is replaced withpressurized nitrogen to prevent moisture from entering the repeaterhousing. To enable the repeater housing to maintain the pressurizednitrogen, it is conventional to route optical fibers entering andexiting the repeater through a seal. One known system for creating theseal includes routing the fibers through a plastic tube on the outsideof the repeater housing. A compressible rubber stopper is then insertedin one end of the plastic tube to seal the end of the plastic tube. Therubber stopper is punctured one hole at a time for each optical fiber inthe bundle and each fiber is routed through a respective hole during thepuncturing process. The compressible nature of the rubber stopper isintended to create an individual seal with each optical fiber. At leastone drawback of this conventional seal and sealing method is that theassembly is labor intensive.

[0004] Additionally, this type of sealing assembly is better suited forwater blockage. Because the sealing assembly relies on a friction fitbetween the rubber stopper and the plastic tube and fibers, the nitrogenin the pressurized housing interior could still potentially escapethrough the seal if tight tolerances are not achieved. Furthermore, thisexisting sealing assembly had difficulty accepting more than eightfibers due to the inherent material properties of the rubber stopper andthe difficulty in drawing the fiber through the rubber. This sealingassembly thus could not easily accommodate the increased number offibers in high fiber count cables.

[0005] Accordingly, there is a need for a gas blocking device that iseasier to install, that has improved sealing properties, and that iscapable of accommodating an increased number of fibers.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, an optical fiber deviceis provided. The optical fiber device comprises a housing that is vacuumdrawn and pressurized with a gas to prevent moisture from entering thehousing. An optical fiber holding tube extends through a wall in thehousing such that a first end of the optical fiber holding tube iscontained in the housing and a second end of the tube is located outsidethe housing. A plurality of optical fibers extends from the first end ofthe optical fiber holding tube to the second end of the optical fiberholding tube without interruption. A gas blocking device is attached tothe first end of the optical fiber holding tube. The optical fibersextend through the gas blocking device and are surrounded by a material,creating a seal that prevents the gas from passing through the opticalfiber holding tube.

[0007] In accordance with another aspect of the present invention, a gasblocking device is provided for use with an optical fiber holding tube.The gas blocking device comprises a fiber containing body having apassageway for receiving a plurality of fibers from the optical fiberholding tube. A material, such as hot melt glue, at least partiallyfills the passageway of the fiber containing body and surrounds theplurality of fibers passing through the passageway. A fiber organizinginsert is secured at one end of the fiber containing body and has aplurality of fiber receiving holes for receiving respective ones of theplurality of fibers. The fiber organizing insert and the fibercontaining body preferably include cooperating key structures such thatthe fiber organizing insert is prevented from rotating with respect tothe fiber containing body. A locking member preferably secures the fiberorganizing insert to the one end of the fiber containing body.

[0008] In one embodiment, the passageway within the fiber containingbody includes a wide portion, a narrow portion, and a tapered portionbetween the narrow portion and the wide portion. The narrow portion ofthe passageway preferably has an inside diameter dimensioned such thatthe fibers act as strength members within the material in the narrowportion. For example, the ratio of the cross-sectional area of thefibers to the cross-sectional area of the narrow portion is about ½. Thefiber organizing insert is secured within the wide portion of thepassageway and is preferably made of a substantially non-compressiblematerial.

[0009] In accordance with a further aspect of the present invention, thegas blocking device is provided as an assembly comprising the fibercontaining body for receiving the fibers and the material, the fiberorganizing insert adapted to be positioned at one end of the fibercontaining body, and the locking member adapted to lock the fiberorganizing insert to the fiber containing body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features and advantages of the present inventionwill be better understood by reading the following detailed description,taken together with the drawings wherein:

[0011]FIG. 1 is a schematic view of one end of a repeater, including agas blocking device according to one embodiment of the presentinvention;

[0012]FIG. 2 is a cross-sectional view of the gas blocking deviceincluding fibers and material, according to one embodiment of thepresent invention

[0013]FIG. 3 is a perspective view of the gas blocking device shown inFIG. 2;

[0014]FIG. 4 is a perspective view of the fiber organizing insert,according to one embodiment of the present invention;

[0015]FIG. 5 is a top plan view of the fiber organizing insert shown inFIG. 4; and

[0016]FIG. 6 is a perspective view of the fiber containing body used inthe gas blocking device shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The gas blocking device 30, FIG. 1, according to the presentinvention, is used to substantially prevent or block the passage of gaswhile allowing optical fibers to pass through. According to theexemplary embodiment, the gas blocking device 30 is used in an opticalfiber repeater 10. The gas blocking device 30 may also be used in otherdevices that house optical fibers, such as a joint box.

[0018] The repeater 10 receives, amplifies, and retransmits signalsbeing carried by a fiber optic cable. Repeater 10 includes a repeaterhousing 12 containing a signal processing and routing system 14 having alaser (not shown). An end cover or wall 20 covers the end of therepeater housing 12, and a cone 16 encloses the end of the repeaterhousing 12. An optical fiber holding tube 18, sometimes referred to as apigtail, extends from inside the repeater housing 12 through the endcover 20 and out of the cone 16. A tube seal 22 is incorporated wherethe fiber holding tube 18 extends through the end cover 20 to make therepeater housing 12 water tight in that area.

[0019] A cable structure (not shown) is connected to the cone 16, andoptical fibers 24 extend from the cable structure through the opticalfiber holding tube 18 to carry signals to and/or from the repeater 10.The fibers 24 exit the end 26 of the optical fiber holding tube 18within a fiber tray 28 inside the repeater housing 12 and are coupled ina known manner to the signal processing and routing system 14. A similararrangement exists at the other end of the repeater 10. This enables thesignals transmitted by the fibers 24 to one end of the repeater 10 to bereceived, amplified and retransmitted to the fibers 24 at the other endof the repeater 10.

[0020] To prevent moisture or condensation from entering the repeaterhousing 12, the repeater housing 12 is vacuum drawn and the air isreplaced with pressurized nitrogen or another suitable gas. The repeaterhousing 12 is typically pressurized to about 30 to 35 psi. The gasblocking device 30 is attached to the end 26 of the optical fiberholding tube 18 inside of the repeater housing 12 and prevents thepressurized gas from exiting the repeater 10 through the optical fiberholding tube 18. The gas blocking device 30 also prevents gas fromentering the repeater 10 through the fiber holding tube 18.

[0021] According to one embodiment, the gas blocking device 30, FIGS. 2and 3, includes an elongated fiber containing body 32, a fiberorganizing insert 34, and a locking member 36. The fibers 24 extendthrough the fiber organizing insert 34 into a passageway through thebody 32 at one end and pass out of the body 32 through the opposite end.The locking member 36 secures the fiber organizing insert 34 to the body32. A material 40, such as hot melt glue, surrounds the fibers 24 withinthe body 32 and seals the passageway around the fibers 24, therebypreventing gas from passing through the body 32. Hot melt glue has thepreferred capability of being re-heated and softened to allow adjustmentof the fibers 24 within the body 32 as needed. Other types of material,such as epoxy or other adhesives, may also be used.

[0022] In one embodiment, the passageway in the fiber containing body 32includes a wide portion 42, a narrow portion 44, and a tapered portion46 therebetween. The wide portion 42 and tapered portion 46 allow thematerial or adhesive 40 to flow into the narrow portion 44 of thepassageway where the sealing takes place. The fibers 24 preferably actas strength members within the material 40 similar to the manner inwhich steel is used to reinforce concrete. For example, when the gasblocking device 30 is frozen, the fibers 24 hold the adhesive 40together and prevent the adhesive 40 from cracking. To allow the fibers24 to act as strength members and provide this reinforcement, the narrowportion 44 of the passageway should not be too wide. The narrow portion44 preferably has an inside diameter just large enough to receive thefibers 24 and to allow the material or adhesive 40 to flow into thenarrow portion 44 and seal the fibers 24. The ratio of thecross-sectional area of the fibers 24 to the cross-sectional area of thenarrow portion 44 is preferably about ½. In one example, the narrowportion 44 may have an inside diameter of about {fraction (1/16)} in.This size is capable of accommodating about 16 to 24 fibers 24. Althoughonly four fibers 24 are shown in FIGS. 2 and 3 for purposes of clarity,it is contemplated that multiple fibers may be used, for example 16 to24 fibers or perhaps even more.

[0023] The adhesive 40 preferably fills at least substantially theentire length of the narrow portion 44 of the passageway. The narrowportion 44 preferably has a minimum length sufficient for pressuresealing purposes. In the exemplary embodiment, the length of the narrowportion 44 is about 1.5 in. Although the exemplary embodiment is shownwith a specific shape, the fiber containing body 32 can have othershapes, sizes and configurations.

[0024] According to one preferred embodiment, the fiber organizinginsert 34, FIG. 4, has a center plug 50 and a seating flange 52 thatseats the fiber organizing insert 34 relative to the fiber containingbody 32 (FIG. 2). The fiber organizing insert 34 includes preformedfiber receiving holes 54 through which the individual optical fibers 24extend and enter into the fiber containing body 32. Although theexemplary embodiment shows the holes 54 arranged as a single circle, thepreformed fiber receiving holes 54 can be arranged in two or moreconcentric circles to accommodate additional fiber 24.

[0025] The fiber organizing insert 34 is preferably made of a rigid,substantially non-compressible material, such as plastic, that will notscratch or damage the fibers and will withstand being heated and frozen.The fiber organizing insert 34 is thus capable of accommodating morefibers than the compressible rubber stoppers used in the conventionalsealing devices. Although plastic is used in the exemplary embodiment,other suitable materials may also be used. The fiber organizing insert34 may also have other shapes, sizes and configurations.

[0026] The fiber organizing insert 34 engages the fiber containing body32 such that the seating flange 52 is seated at the end of the fibercontaining body 32 and the center plug 50 extends into the wide portion42 (see FIG. 2). The fiber organizing insert 34 and the fiber containingbody 32 preferably include cooperating key structures for preventingrotation of the fiber organizing insert 34 with respect to the fibercontaining body 32. By preventing rotation when the fiber organizinginsert 34 is engaged with the fiber containing body 32, the cooperatingkey structures prevent undesirable twisting of the fibers 24. The fiberorganizing insert 34 thus organizes and restrains the fibers 24 toprevent microbending and other damage to the fibers 24.

[0027] According to the exemplary embodiment of the cooperating keystructures, shown in FIG. 5, a locking key 56 on the fiber containingbody 32 engages a locking recess 58 in the seating flange 52 of thefiber organizing insert 34. The locking key 56 preferably extends fromthe end of the fiber containing body 32, as shown in FIG. 6. The fiberorganizing insert 34 preferably includes multiple locking recesses 58 tofacilitate positioning of the fiber organizing insert 34.

[0028] Although one embodiment of the cooperating key structures isshown and described, any arrangement of cooperating key structurescapable of preventing rotation may be used. For example, the fiberorganizing insert 34 may include a single locking recess 58 or the fibercontaining body may include multiple locking keys 56. Alternatively, thefiber organizing insert 34 may have keys or projections engagingrecesses in the fiber containing body 32.

[0029] The fiber organizing insert 34 is secured against the fibercontaining body 32 by the locking member 36 (see FIG. 2). The lockingmember 36 includes an inner extending flange 60 extending over the endof the body 32 and a base 62 extending around the outside of the body32. The base 62 of the locking member 36 is secured to the fibercontaining body 32, for example, by a threaded engagement. According tothe exemplary embodiment, the base 62 has a shaped portion 64 (e.g.,hexagonal) that may interface with a tool, such as a wrench. The lockingmember 36 may also be attached to the fiber containing body 32 in otherways. When the locking member 36 is secured to the body 32, the innerextending flange 60 bears against the fiber organizing insert 34 toeffectively sandwich the fiber organizing insert 34 between the lockingmember 36 and the fiber containing body 32.

[0030] To assemble the gas blocking device 30, the fiber containing body32 is secured to the end 26 of the fiber holding tube 18. The fibercontaining body 32 and the fiber holding tube 18 are both preferablymade of copper and may be secured by soldering. Although copper ispreferred because of its good conductability, other materials may alsobe used. The fibers 24 are inserted into the fiber organizing insert 34and the fiber containing body 32. Each of the fibers 24 is insertedthrough one of the fiber receiving holes 54 in the fiber organizinginsert 34.

[0031] With the fiber organizing insert 34 positioned just above thelocking key 56 of the fiber containing body 32, the hot melt glue (orother suitable adhesive) is injected into the fiber containing body 32until the hot melt glue substantially fills the narrow portion 44. Thefiber organizing insert 34 is then moved into place such that thelocking key 56 engages one of the recesses 58. The locking member 36 isthen positioned over the fiber organizing insert 34 and threaded ontothe fiber containing body 32 to secure the fiber organizing insert 34 tothe body 32. The fiber holding tube 18 with the gas blocking device 30is then installed into the repeater housing 12 with the gas blockingdevice 30 and fibers 24 exiting the gas blocking device 30 being stowedin the fiber tray 28.

[0032] Accordingly, the gas blocking device of the present invention isrelatively easy to install and is more effective at blocking gascompared to conventional sealing devices.

[0033] Modifications and substitutions by one of ordinary skill in theart are considered to be within the scope of the present invention,which is not to be limited except by the claims that follow.

What is claimed is:
 1. An optical fiber device comprising: a housinghaving a wall, wherein said housing is vacuum drawn and pressurized witha gas to prevent moisture from entering said housing; an optical fiberholding tube extending through said wall and having a first end and asecond end, said first end of said optical fiber holding tube containedin said housing and said second end of said optical fiber holding tubelocated outside of said housing; a plurality of optical fibers extendingfrom said first end of said optical fiber holding tube to said secondend of said optical fiber holding tube without interruption; and a gasblocking device attached to said first end of said optical fiber holdingtube, wherein said optical fibers extend through said gas blockingdevice, and wherein said gas blocking device contains materialsurrounding said optical fibers such that said gas blocking devicecreates a seal substantially preventing gas from passing through saidoptical fiber holding tube.
 2. The optical fiber device according toclaim 1, wherein said gas is nitrogen.
 3. The optical fiber deviceaccording to claim 1, further including a water seal sealing aninterface between said wall and said optical fiber holding tubeextending through said wall.
 4. The optical fiber device according toclaim 1 wherein said gas blocking device includes: a fiber containingbody having a passageway containing said plurality of fibers; and afiber organizing insert secured at one end of said fiber containing bodysuch that said fiber organizing insert is prevented from rotating withrespect to said fiber containing body, wherein said fiber organizinginsert includes a plurality of fiber receiving holes each receivingrespective ones of said plurality of fibers.
 5. The optical fiber deviceaccording to claim 4, further including a locking member securing saidfiber organizing insert to said one end of said fiber containing body.6. The optical fiber device according to claim 4, wherein saidpassageway in said fiber containing body includes a wide portion, anarrow portion, and a tapered portion between said wide portion and saidnarrow portion, and wherein said fiber organizing insert is securedwithin said wide portion.
 7. The optical fiber device according to claim4, wherein said fiber organizing insert is made of a substantiallynon-compressible material.
 8. The optical fiber device according toclaim 4, wherein said fiber containing body and said fiber holding tubeare made of a conductive metal and are soldered together.
 9. The opticalfiber device according to claim 1, wherein said material is hot meltglue.
 10. A gas blocking device for use at one end of an optical fiberholding tube holding a plurality of fibers, said gas blocking devicecomprising: a fiber containing body having a passageway, wherein saidplurality of fibers pass from said optical fiber holding tube throughsaid passageway; a material for least partially filling said passagewayof said fiber containing body and surrounding said plurality of fiberspassing through said passageway; and a fiber organizing insert securedat one end of said fiber containing body and being prevented fromrotation with respect to said fiber containing body, wherein said fiberorganizing insert has a plurality of fiber receiving holes eachreceiving respective ones of said plurality of fibers.
 11. The gasblocking device according to claim 10, wherein said fiber organizinginsert is made of a substantially non-compressible material.
 12. The gasblocking device according to claim 10, further including a lockingmember securing said fiber organizing insert to said one end of saidfiber containing body.
 13. The gas blocking device according to claim10, wherein said passageway in said fiber containing body includes anarrow portion having an inside diameter dimensioned such that saidfibers act as strength members within said adhesive in said narrowportion of said passageway.
 14. The gas blocking device according toclaim 13, wherein the ratio of the cross-sectional area of said fibersto the cross-sectional area of said narrow portion is about ½.
 15. Thegas blocking device according to claim 13, wherein said passageway insaid fiber containing body includes a wide portion and a tapered portionbetween said wide portion and said narrow portion.
 16. The gas blockingdevice according to claim 15 wherein said material is hot melt glue. 17.A gas blocking device assembly for use with an optical fiber holdingtube holding a plurality of optical fibers, said gas blocking deviceassembly comprising: a fiber containing body having a passageway forreceiving said plurality of fibers from said optical fiber holding tubeand for receiving a material to seal said fibers; a fiber organizinginsert adapted to be positioned at one end of said fiber containingbody, wherein said fiber organizing insert includes a plurality ofpreformed fiber receiving holes for receiving respective ones of saidplurality of fibers, wherein said fiber organizing insert and said fibercontaining body include cooperating key structures for preventingrotation of said organizing insert when positioned at said one end ofsaid fiber containing body; and a locking member adapted to lock saidfiber organizing insert to said one end of said fiber containing body.18. The gas blocking device assembly according to claim 17, wherein saidcooperating key structures include at least one recess in said fiberorganizing insert and at least one locking key projecting from said oneend of said fiber containing body.
 19. The gas blocking device assemblyaccording to claim 17, wherein said fiber organizing insert is made of asubstantially non-compressible material.
 20. The gas blocking deviceassembly according to claim 17, wherein said passageway in said fibercontaining body includes a wide portion, a narrow portion, and a taperedportion between said narrow portion and said wide portion, and whereinsaid wide portion is adapted to receive said fiber organizing insert.